Dragon Ball Series
There are 3 parts to the Dragon Ball series. They are...
Goku has come to Earth from Planet Vegeta. His grandfather, Gohan, has passed away and has left Goku to continue life. Dragon Ball starts from here.
This part, Dragon Ball Z, introduces many new charaters. For example, Gohan, Cell, Buu. It also reveals Goku's identity. Who he is, where he came from. This is the main part of the series. I don't think the "Z" has a significant meaning. Zetta or Zen.. I don't know how the pronounce it. This is probably the best one of the three.
This part, Dragon Ball GT is pretty short. Only 64 episodes long. It shows one of Goku's old enemies, Emporer Pilaf. Remember that retard? =P Well.. this part is short, but it has quite a lot of action. In space, on Earth.. the battles against Baby, Super 17 and even Shenron. This is where Dragon Ball ends.
